An image heating device includes first and second heating elements, a temperature detection element, and an electric power controller. The electric power controller controls electric power to be supplied to the both heating elements for each control cycle corresponding to a period including a plurality of consecutive half cycles of alternate current per a detected temperature. The electric power controller controls electric power such that a current having a waveform including first half cycles and a second half cycle is supplied to both heating elements. The electric power controller sets a first control pattern such that the first and second half cycles overlap with each other in the half cycles of same phases in supplied alternate current and sets a second control pattern such that the first half cycles overlap with each other and the second half cycles overlap with each other in the half cycles of the same phases.
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1. An image heating device comprising: a first heating element;
a second heating element configured to be driven independently from the first heating element;
a temperature detection element configured to detect a temperature; and an electric power controller configured to control electric power to be supplied to the first and second heating elements for each control cycle corresponding to a period including a plurality of consecutive hall cycles of alternate current in accordance with a temperature detected by the temperature detection element,
wherein the electric power controller controls electric power such that a current is supplied to both the first and second heating elements, wherein the current includes a waveform having first half cycles, in which current is supplied or not supplied in entire half cycles of alternate current, and a second half cycle, in which current is supplied to portions of the half cycles of alternate current in a mixed manner,
wherein the electric power controller sets a first control pattern in which electric power is controlled such that the first half cycle supplied to the first heating element and overlaps with the second half cycle supplied to the second heating element and in the half cycles of same phases, and the second half cycle supplied to the first heating element overlaps with the first half cycle supplied to the second heating element in the half cycles of the same phases during the control cycle; and
wherein the electric power controller sets a second control pattern in which electric power is controlled such that the first half cycles supplied to the first and second heating elements overlap with each other and the second half cycles supplied to the first and second heating elements overlap with each other in the half cycles of the same phases during the control cycle.
9. An image heating device comprising:
a first heating element;
a second heating element configured to be driven independently from the first heating element;
a temperature detection element configured to detect a temperature; and
an electric power controller configured to control electric power to be supplied to the first and second heating elements for each control cycle corresponding to a period including a plurality of consecutive half cycles of alternate current in accordance with a temperature detected by the temperature detection element,
wherein heat distribution of the first heating element and heat distribution of the second heating element are different from each other,
wherein the electric power controller controls electric power such that a current is supplied to both the first and second heating elements, wherein the current includes a waveform having first half cycles, in which current is supplied or not supplied in entire half cycles of alternate current, and a second half cycle, in which current is supplied to portions of the half cycles of alternate current in a mixed manner,
wherein the electric power controller sets a first control pattern in which electric power is controlled such that the first half cycle supplied to the first heating element overlaps with the second half cycle supplied to the second heating element in the half cycles of same phases, and the second half cycle supplied to the first heating element overlaps with the first half cycle supplied to the second heating element in the half cycles of the same phases, and sets a second control pattern in which electric power is controlled such that the first half cycles supplied to the first and second heating elements overlap with each other and the second half cycles supplied to the first and second heating elements overlap with each other in the half cycles of the same phases, and
wherein the electric power controller is configured to changing a ratio (x:Y) of a duty ratio of electric power to be supplied to the first heating element to a duty ratio of electric power to be supplied to the second heating element,
wherein a duty ratio of electric power to be set for each control cycle in accordance with a temperature detected by the temperature detection element is denoted by P (%),
wherein a larger value between x and Y is denoted by Z,
wherein the duty ratio of electric power to be supplied to the first heating element is denoted by Px (%)=(x/Z)×P (%),
wherein the duty ratio of electric power to be supplied to the second heating element is denoted by Py (%)=(Y/Z)×F (%), and
wherein, when both of the duty ratio Px and the duty ratio Py are larger than a threshold value or smaller than the threshold value, the electric power controller controls electric power to be supplied to the first and second heating elements by the first control pattern, and
wherein, when one of the duty ratio Px and the duty ratio Py is larger than the threshold value and the other of the duty ratio Px and the duty ratio Py is smaller than the threshold value, the electric power controller controls electric power to be supplied to the first and second heating elements by the second control pattern.
13. A method for an image heating device having a first heating element, a second heating element, a temperature detection element, and an electric power controller, the method comprising:
driving the second heating element independently from the first heating element;
detecting a temperature via the temperature detection element; and
controlling, via the electric power controller, electric power to be supplied to the first and second heating elements for each control cycle corresponding to a period including a plurality of consecutive half cycles of alternate current in accordance with a temperature detected by the temperature detection element,
wherein heat distribution of the first heating element and heat distribution of the second heating element are different from each other,
wherein controlling electrical power includes controlling electric power such that a current is supplied to both the first and second heating elements, wherein the current includes a waveform having first half cycles, in which current is supplied or not supplied in entire half cycles of alternate current, and a second half cycle, in which current is supplied to portions of the half cycles of alternate current in a mixed manner,
wherein controlling electrical power includes setting a first control pattern in which electric power is controlled such that the first half cycle supplied to the first heating element overlaps with the second half cycle supplied to the second heating element in the half cycles of same phases, and the second half cycle supplied to the first heating element overlaps with the first half cycle supplied to the second heating element in the half cycles of the same phases during the control cycle,
wherein controlling electrical power includes setting a second control pattern in which electric power is controlled such that the first half cycles supplied to the first and second heating elements overlap with each other and the second half cycles supplied to the first and second heating elements overlap with each other in the half cycles of the same phases during the control cycle,
wherein the electric power controller is configured to changing a ratio (x:Y) of a duty ratio of electric power to be supplied to the first heating element to a duty ratio of electric power to be supplied to the second heating element,
wherein a duty ratio of electric power to be set for each control cycle in accordance with a temperature detected by the temperature detection element is denoted by P (%),
wherein a larger value between x and Y is denoted by Z,
wherein the duty ratio of electric power to be supplied to the first heating element is denoted by Px (%)=(x/Z)×P (%),
wherein the duty ratio of electric power to be supplied to the second heating element is denoted by Py (%)=(Y/Z)×P (%), and
wherein, when both of the duty ratio Px and the duty ratio Py are larger than a threshold value or smaller than the threshold value, controlling electric power via the electric power controller includes controlling electric power to be supplied to the first and second heating elements by the first control pattern, and
wherein, when one of the duty ratio Px and the duty ratio Py is larger than the threshold value and the other of the duty ratio Px and the duty ratio Py is smaller than the threshold value, controlling electric power via the electric power controller includes controlling electric power to be supplied to the first and second heating elements by the second control pattern.
2. The image heating device according to
3. The image heating device according to
wherein the electric power controller is configured to changing a ratio (x:Y) of a duty ratio of electric power to be supplied to the first heating element to a duty ratio of electric power to be supplied to the second heating element,
wherein a duty ratio of electric power to be set for each control cycle in accordance with a temperature detected by the temperature detection element is denoted by P (%),
wherein a larger value between x and Y is denoted by Z,
wherein the duty ratio of electric power to be supplied to the first heating element is denoted by Px (%)=(x/Z)×P (%),
wherein the duty ratio of electric power to be supplied to the second heating element is denoted by Py (%)=(Y/Z)×P (%), and
wherein, when both of the duty ratio Px and the duty ratio Py are larger than a threshold value or smaller than the threshold value, the electric power controller controls electric power to be supplied to the first and second heating elements by the first control pattern, and
wherein, when one of the duty ratio Px and the duty ratio Py is larger than the threshold value and the other of the duty ratio Px and the duty ratio Py is smaller than the threshold value, the electric power controller controls electric power to be supplied to the first and second heating elements by the second control pattern.
4. The image heating device according to
wherein the electric power controller is configured to changing a ratio (x:Y) of a duty ratio of electric power to be supplied to the first heating element to a duty ratio of electric power to be supplied to the second heating element, and
wherein the electric power controller selects one of the first and second control patterns in accordance with a variation amount of sums of electric powers (W1) of the first heating element and electric powers (W2) of the second heating element for individual half cycles in a period corresponding to the control cycle.
5. The image heating device according to
6. The image heating device according to
7. The image heating device according to
8. The image heating device according to
10. The image heating device according to
11. The image heating device according to
12. The image heating device according to
14. The method according to
15. The method according to
16. The method according to
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1. Field of the Invention
The present invention relates to an image heating device suitably used as a fixing device included in an image forming apparatus employing an electrophotography recording technique.
2. Description of the Related Art
A fixing device included in an image forming apparatus employing an electrophotography recording technique generally includes a heater. The heater is connected to an AC power source through a switching element such as a triac, and electric power is supplied from the AC power source so that the heater generates heat.
When the heater (a heating element) is controlled, a harmonic current and a flicker are required to be suppressed. Japanese Patent Laid-Open Nos. 2005-195640 and 2011-95314 disclose methods for suppressing generation of a harmonic current and a flicker in a fixing device including a plurality of heaters. Specifically, a waveform in which a first half cycle in which current is supplied or not supplied in entire half cycles of alternate current and a second half cycle in which current is supplied in portions of half cycles of the alternate current are mixed is applied to two heaters which may be independently driven. Furthermore, the alternate current supplied to one of the heaters and the alternate current supplied to the other of the heaters are controlled such that the first and second half cycles overlap with each other in half cycles of the same phases of the alternate current supplied to the two heaters. This control is advantageous since synthesized current supplied to the two heaters becomes similar to a sine wave, and therefore, a power factor is improved.
In some fixing devices including a plurality of heaters, for example, a fixing device disclosed in Japanese Patent No. 4208772, a power supply ratio between heaters is changed in accordance with a size of a recording material and different heat generation distributions are set.
Here, when the control methods disclosed in Japanese Patent Laid-open Nos. 2005-195640 and 2011-95314 are employed in an apparatus which changes a power supply ratio between heaters in accordance with a size of a recording material, such as the apparatus disclosed in Japanese Patent No. 4208772, the following problem arises. That is, when a recording material of a small size is subjected to a fixing process, electric power to be supplied to one of heaters is required to be reduced in order to suppress a heat generation amount in a region in which the recording material does not pass. However, it is found that electric power is concentrated on certain half cycles of an AC waveform and a flicker is further generated.
The present invention provides an image heating device which supports a case where improvement of a power factor is preferentially performed or a case where suppression of a flicker is preferentially performed. An electric power controller may set a first control pattern in which electric power is controlled such that first half cycles in which current is supplied or not supplied in entire half cycles of alternate current and second half cycles in which current is supplied portions of portions of half cycles of alternate current overlap with each other in half cycles of the same phases in the alternate current supplied to the first heating element and the alternate current supplied to the second heating element and a second control pattern in which electric power is controlled such that the first half cycles overlap with each other and the second half cycles overlap with each other in the half cycles of the same phases. According to an aspect of the present invention, the image heating device includes a first heating element, a second heating element configured to be driven independently from the first heating element, a temperature detection element configured to detect a temperature, and an electric power controller configured to control electric power to be supplied to the first and second heating elements for each control cycle corresponding to a period including a plurality of consecutive half cycles of alternate current in accordance with a temperature detected by the temperature detection element. The electric power controller controls electric power such that a current having a waveform including first half cycles, in which current is supplied or not supplied in entire half cycles of alternate current, and a second half cycle, in which current is supplied to portions of the half cycles of alternate current in a mixed manner, is supplied to both the first and second heating elements. The electric power controller sets a first control pattern in which electric power is controlled such that the first and second half cycles overlap with each other in the half cycles of the same phases in the alternate current supplied to the first heating element and the alternate current supplied to the second heating element and sets a second control pattern in which electric power is controlled such that the first half cycles overlap with each other and the second half cycles overlap with each other in the half cycles of the same phases.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Embodiments of the present invention will be described in detail hereinafter with reference to the accompanying drawings. Here, sizes, materials, and shapes of components and relative arrangements of the components described in the embodiments may be appropriately modified in accordance with configurations and various conditions of an apparatus to which the present invention is applied. Specifically, the scope of the present invention is not limited to the embodiments below.
A controller 31 (including an electric power controller) of the image forming apparatus includes a CPU (Central Processing Unit) 32 including a ROM 32a, a RAM 32b, and a timer 32c, various input/output control circuits (not illustrated), and the like.
The backup roller 103 is driven in a direction indicated by an arrow mark illustrated in
Similarly, the second heating element 112 includes heating sections 112a, electrodes 112c and 112d, and a conductive section 112b which connects the heating sections 112a to the electrodes 112c and 112d and connects the heating sections 112a to each other. The heating sections 112a generate heat when electric power is supplied through the electrodes 112c and 112d. Furthermore, the power supply is performed through power supply connectors 114 and 115. The first and second heating elements 111 and 112 are disposed on the ceramic substrate 110 which is in contact with an inner surface of the endless belt 102. The first and second heating elements 111 and 112 may be independently driven.
A line B illustrated in
The CPU 32 executes heater driving control and the like. The CPU 32 includes input/output ports, the ROM 32a, and the RAM 32b. Reference numerals 60 and 70 represent phase control circuits (heater driving circuits). The first heater driving circuit 60 drives the first heating element 111 and is controlled in accordance with a signal supplied from the CPU 32. The second heater driving circuit 70 drives the second heating element 112 and is controlled in accordance with a signal supplied from the CPU 32.
A temperature of the heater 100 is monitored by a temperature detection element (a thermistor) 54. The temperature detection element 54 is used to detect a temperature of a region of the heater 100 in which a sheet of a minimum size which is usable by the image forming apparatus passes. The temperature detection element 54 has one terminal connected to the ground and the other terminal connected to an electrical resistance 55. The temperature detection element 54 is further connected to an analog input port AN0 of the CPU 32 through an electrical resistance 56. The temperature detection element 54 has a characteristic in which when the temperature detection element 54 is heated, a resistance value is lowered. The CPU 32 stores a temperature table (not illustrated), and detects a temperature of the heater 100 in accordance with divided voltages of a resistance of the temperature detection element 54 and the fixed electrical resistance 55.
Electric power output from the commercial power source 50 is supplied to a ZEROX generation circuit 57 through the AC filter 52. The ZEROX generation circuit 57 outputs a signal in a high level when a commercial power source voltage is equal to or smaller than a threshold value voltage set in the vicinity of a voltage of 0V, and otherwise outputs a signal in a low level. Thereafter, a pulse signal having a cycle substantially equal to a cycle of the commercial power source voltage is supplied through an electrical resistance 58 to a port PA1 of the CPU 32. The CPU 32 detects an edge of a ZEROX signal in which the ZEROX signal is changed from a high level to a low level, and uses the edge as a reference timing for driving the first and second heater driving circuits 60 and 70.
The CPU 32 determines a duty ratio Px of electric power to be supplied to the first heating element 111 and a duty ratio Py of electric power to be supplied to the second heating element 112 in accordance with the temperature detected by the temperature detection element 54 and a sheet size (a sheet width). Then the CPU 32 determines timings when the first and second heater driving circuits 60 and 70 are driven so that the electric power to be supplied to the first and second heating elements 111 and 112 attains the duty ratios Px and Py and outputs driving signals Drive1 and Drive2 from ports PA2 and PA3.
Next, the first phase control circuit 60 will be described. Since the second phase control circuit 70 is configured similarly to the first phase control circuit 60, a detailed description of the second phase control circuit 70 is omitted. When the output port PA2 (PA3) is brought to a high level at a timing determined by the CPU 32, a transistor 65 (75) is turned on through a base resistance 67 (77). When the transistor 65 (75) is turned on, a phototriac coupler 62 (72) is turned on. Note that the phototriac coupler 62 (72) is a device which ensures a creeping distance between the primary side and the secondary side. An electrical resistance 66 (76) is used to restrict current supplied to a light-emitting diode included in the phototriac coupler 62 (72).
Electrical resistances 63 (73) and 64 (74) are bias resistances for a triac 61 (71), and when the phototriac coupler 62 (72) is turned on, the triac 61 (71) is turned on. The triac 61 (71) maintains an on state after being turned on until an AC voltage reaches a next zerocross point. Accordingly, electric power is supplied to the main heating element 111 (the sub heating element 112) in accordance with a timing of the on state.
The CPU 32 is capable of changing a ratio (X:Y) of the duty ratio of the electric power to be supplied to the first heating element 111 to the duty ratio of the electric power to be supplied to the second heating element 112. In this embodiment, the ratio of the duty ratio of the electric power to be supplied to the main heating element 111 to the duty ratio of the electric power to be supplied to the sub heating element 112 is set in accordance with the width of the sheet 21. For example, when printing is performed on the sheet 21 having a width of L2 illustrated in
In this embodiment, ratios (X:Y) of standard sizes are illustrated in Table 1. In Table 1, the term “lateral” represents a case where a sheet is conveyed such that a long side of the sheet is parallel to the fixing nip portion N (Long Edge Feed). In Table 1, the term “longitudinal” represents a case where a sheet is conveyed such that a short side of the sheet is parallel to the fixing nip portion N (Short Edge Feed).
TABLE 1
Sheet Size
X:Y
A4 lateral, A3 longitudinal
100:100
LTR lateral, LDR longitudinal,
100:50
B4 longitudinal, EXE lateral,
B5 lateral
LTR longitudinal,
100:10
LGL longitudinal
A4 longitudinal, A5 lateral,
100:0
A6 longitudinal
The ratio (X:Y) may be more finely set in accordance with a size of a sheet, and the ratio (X:Y) may be set in accordance with a value of a sheet width specified by a user or a sheet width measured by a sheet width detection unit, not illustrated, in a case of a sheet of an unstandardized size. Alternatively, a second temperature detection element which detects a temperature of edge portions in a longitudinal direction of the heater 100 (a sheet non-passing portion of a minimum size sheet) may be provided and the ratio (X:Y) may be set in accordance with the temperature detected by the second temperature detection element.
The CPU 32, first, calculates a duty ratio P (%) (=Duty Cycle) in accordance with a temperature detected by the temperature detection element 54. When the duty ratio P (%) and the ratio (X:Y) corresponding to a sheet size are determined, the CPU 32 calculates a duty ratio Px (%) of electric power to be supplied to the first heating element 111 and a duty ratio Py (%) of electric power to be supplied to the second heating element 112. The duty ratio Px is represented by the following expression: Px (%)=(X/Z)×P, and the duty ratio Py is represented by the following expression: Py (%)=(Y/Z)×P. Note that “Z” corresponds to a larger one of “X” and “Y”.
As illustrated in
Furthermore, the case of
The duty ratio P (%) of the electric power is calculated by the CPU 32 using PID control or the like in accordance with the temperature detected by the temperature detection element 54 and a target temperature set in advance. The duty ratio P (%) is set for individual control cycles in accordance with temperatures detected by the temperature detection element 54.
When the duty ratio P is 75% and the ratio (X:Y) is 100:100, Z is 100. Accordingly, electric power of the duty ratio Px of 75% (Px=100/100*75) is supplied to the main heating element 111. Furthermore, electric power of the duty ratio Py of 75% (Py=100/100*75) is supplied to the sub heating element 112. A waveform 401 represents a current supplied to the main heating element 111, a waveform 402 represents a current supplied to the sub heating element 112, and a waveform 403 represents a synthesized wave obtained by synthesizing the current supplied to the main heating element 111 and the current supplied to the sub heating element 112.
As with
When the duty ratios Px and Py become smaller than 50%, a first half cycle in which current is not supplied is set in the control cycle. Furthermore, in a case of the first control pattern, a half cycle (of alternate current supplied to the other heating element) having a phase the same as that of the first half cycle in which current is not supplied correspond to a second half cycle in which current is supplied in a portion of the half cycle. A current value of a synthesized wave of the first half cycle in which current is not supplied and the second half cycle in which current is supplied in a portion of the half cycle is small as illustrated in
On the other hand, when the duty ratios Px and Py become larger than 50%, a first half cycle in which current is supplied in an entire half cycle is set in the control cycle. In a case of the first control pattern, a half cycle having a phase the same as that of the first half cycle in which current is supplied in the entire half cycle corresponds to a second half cycle in which current is supplied in a portion of the half cycle. A current value of a synthesized wave of the first half cycle in which current is supplied in the entire half cycle and the second half cycle in which current is supplied in a portion of the half cycle is large as illustrated in
As described above, when one of the duty ratios Px and Py is smaller than 50% and the other is larger than 50%, current is concentrated on some half cycles of the synthesized wave (half cycles represented by “large”) and considerably small current is obtained in the other half cycles (half cycles represented by “small”) as illustrated in
On the other hand, when the waveform illustrated in
However, when the second control pattern is employed, the power factor and the harmonic wave are deteriorated. Accordingly, the second control pattern is employed only in a case where one of the duty ratios Px and Py is smaller than 50% and the other is larger than 50%. Here, in a case where the second control pattern is preferably employed, even though the power factor is deteriorated, supplied power is low and a maximum consumption current is small, and accordingly, there arises no problem.
Subsequently, the CPU 32 detects a ZEROX signal (S108) and starts power supply (S109) at a timing when a rising edge or a falling edge of the ZEROX signal is detected. In step S109, power supply to the main heating element 111 and the sub heating element 112 is started using the duty ratio Px (%) and the duty ratio Py (%), respectively, in accordance with the first control pattern. It is determined whether N is equal to 8, that is, whether a control cycle is terminated in step S110. When the determination is negative, the CPU 32 increments N (5111). When N is equal to 8, a next power supply cycle (a next control cycle) is entered (the process returns from step S112 to step S101). When it is determined that the power supply is terminated in step S112, the power control sequence is terminated.
When the determination is affirmative in step S105, the second control pattern illustrated in
As described above, the CPU 32 (the electric power controller) selects the first control pattern or the second control pattern in accordance with the calculated duty ratios Px and Py. In
As is apparent from the foregoing description, the case where the first control pattern is selected corresponds to the case where both of the duty ratios Px and Py are equal to or larger than 51% or the case where both of the duty ratios Px and Py are equal to or smaller than 50%. In the first control pattern illustrated in
On the other hand, the case where the second control pattern is selected corresponds to the case where the duty ratio Px is equal to or larger than 51% and the duty ratio Py is equal to or smaller than 50% or the case where the duty ratio Px is equal to or smaller than 50% and the duty ratio Py is equal to or larger than 51%. In the second control pattern illustrated in
As described above, in this embodiment, one of the first and second control patterns may be selected. Accordingly, an image heating device which supports a case where improvement of a power factor is preferentially performed and a case where suppression of a flicker is preferentially performed may be provided.
Furthermore, when both of the duty ratios Px and Py are larger than a threshold value or smaller than the threshold value, the power controller controls electric power such that the first half cycles and the second half cycles overlap with each other in the half cycles of the same phases of alternate current supplied to the first heating element 111 and alternate current supplied to the second heating element 112. Furthermore, When one of the duty ratios Px and Py is larger than the threshold value and the other is smaller than the threshold value, the power controller controls electric power such that the first half cycles overlap with each other and the second half cycles overlap with each other in the half cycles of the same phases. By this control, even in an apparatus which is required to change the ratio (X:Y), improvement of a power factor and suppression of generation of a flicker may be both attained.
In the first embodiment, the second control pattern is selected when a combination of the duty ratio Px (%) of electric power to be supplied to the main heating element 111 and the duty ratio Py (%) of electric power to be supplied to the sub heating element 112 satisfies a specific condition.
In a second embodiment, a determination as to whether a control pattern is to be changed is made by calculating electric power for each half cycle which is actually supplied to a main heating element and a sub heating element and further calculating variation of the electric power in a control cycle.
A power control circuit of this embodiment will be described with reference to
A current I 1001 of
A reference numeral 1005 of
After a block of half wave rectification performed by the diode 203 is terminated, current to be supplied to the capacitor 214 for electric charge is stopped, and therefore, a voltage value is subjected to peak hold as denoted by a reference numeral 1006 of
Specifically, a peak hold voltage Vlf of the capacitor 214 corresponds to an integral value of a square value, corresponding to a half cycle, of a waveform obtained by performing voltage conversion on a current waveform by the current transformer 80 on the secondary side. The voltage value which has been subjected to the peak hold performed by the capacitor 214 is supplied from the heater current detection circuit 81 to the CPU 32 as an HCRRT1 signal 1006. The CPU 32 performs A/D conversion on the HCRRT1 signal 1006 input to a port PA4 for a period from the rising edge of the ZEROX signal 1002 to a certain point after Tdly. A heater current obtained by the A/D conversion corresponds to a heater current for a full wave (one cycle) of commercial power voltage. The CPU 32 averages heater currents of four full waves (four cycles) of commercial power voltage and multiplies a resultant value by a predetermined coefficient so as to calculate electric power to be consumed by the first heating element 111 and the second heating element 112. Note that a method for detecting current is not limited to this.
Next, a power measurement sequence based on current detection according to this embodiment will be described. This sequence is performed in an initial sequence or the like when a printer is turned on, for example. Furthermore, this sequence aims at calculating electric power supplied to the main heating element 111 and the sub heating element 112 while the duty ratios thereof are 100%.
As described above, in the second embodiment, a determination as to whether a control pattern is to be changed is made by calculating electric power of half cycles which are actually supplied to a main heating element and a sub heating element and further calculating variation of the electric power in a control cycle.
Next, the CPU 32 compares the average value ΔP of the electric power variation amounts and a predetermined electric power variation amount ΔPtgt corresponding to a situation in which a flicker is further generated so as to determine whether the control pattern is to be changed in step S209. Specifically, when power variation in adjacent half cycles is large, it is highly likely that a flicker is generated, and therefore, a second control pattern of the same duty ratios Px and Py is selected. A process from step S211 to step S215 is the same as the process from step S108 to step S112, and therefore, a description thereof is omitted.
As described above, also in this embodiment, the first control pattern or the second control pattern may be selected. Accordingly, an image heating device which supports a case where improvement of a power factor is preferentially performed and a case where suppression of a flicker is preferentially performed may be provided.
Furthermore, in this embodiment, a determination as to whether the control pattern is to be changed is made in accordance with a power variation amount between adjacent half cycles obtained in accordance with a current value of a detected current actually supplied to the heater. Specifically, the first control pattern or the second control pattern is selected in accordance with a variation amount obtained from sums of electric powers (W) of the first heating element 111 for individual half cycles and electric powers (W) of the second heating element 112 for individual half cycle in a control cycle. Accordingly, reliability of selection of a control pattern is improved when compared with the first embodiment.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2013-102396 filed May 14, 2013, which is hereby incorporated by reference herein in its entirety.
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